I have 3, all of which are musically related... although it is not obvious to others that they are.
2 of them have been adapted from album artwork (not cover art), my tattooist changed them to make them fit the location better. The first one is a very small section of album artwork from 19 years ago. I decided I wanted that one done 18 years ago. My first one was only done just before my 34th Birthday though.
Although they are based on music (there is also a theme of religion and hypocrisy developing), they are abstract enough and personal enough that I am fairly sure that they will be unique. I agree that you should avoid band logos and things like that with haste, but if you are sure you are happy with them, why not...?!
I have a few more in planning, again all musical. All bands that I have been into for many, many years.
Music has been my obsession all my life, there is no other logical theme.